1. Field of the Invention:
The present invention relates to an engine, and more particularly to an in-line, multicylinder outboard engine equipped with intake/fuel supply devices.
2. Description of the Relevant Art:
Outboard engines which are detachably mounted on the stern of ships or boats outside of the hull should preferably be small in size and yet capable of producing high output power. Generally, many outboard engines as installed on vessels have cylinders oriented such that their axes lie horizontally and crankshafts are directed vertically. One problem of conventional outboard engines is that intake/fuel supply devices associated therewith are so located as to prevent the engines from operating with sufficient performance capability and also to increase the external dimensions of the engines.
One known multicylinder outboard engine is disclosed in Japanese Laid-Open Utility Model Publication No. 62-124229 published on Aug. 7, 1987. The disclosed engine has a pair of upper and lower cylinders and an intake/fuel supply device disposed on one side of the upper cylinder. The intake/fuel device includes a carburetor coupled to the cylinders through a pair of intake manifolds, for supplying and distributing an air-fuel mixture to the cylinders.
Japanese Laid-Open Utility Model Publication No. 62-184163 published on Nov. 21, 1987 also discloses an outboard engine of a V-shaped multicylinder configuration. The engine includes a pair of V-shaped banks of vertically arranged cylinders. As many carburetors as the number of cylinder pairs are disposed in the cylinder banks for supplying and distributing an air-fuel mixture to the cylinders through an intake manifold.
With the two-cylinder outboard engine disclosed in the former publication, no serious problem arises from the fact that an air-fuel mixture is distributed from the single carburetor to the upper and lower cylinders. However, if an air-fuel mixture is supplied from a single carburetor to more engine cylinders, then the air-fuel mixture may not be distributed uniformly to the engine cylinders since the pipes connecting the intake manifold to the respective cylinders have different lengths. More specifically, if the intake manifold pipes connecting the carburetor to the engine cylinders have different lengths, then the air-fuel ratio of the air-fuel mixture in the intake manifold pipes varies due to air-fuel mixture flows along the manifold walls, resulting in difficulty supplying the air-fuel mixture at an appropriate air-fuel ratio to the cylinders. As a consequence, no stable engine response is achieved especially while the engine is idling. The carburetor is usually positioned higher than the intake ports of the engine cylinders in order to prevent the fuel from being trapped in the intake manifold. One solution is to employ a vertical array of carburetors along the array of the cylinders. However, the size of such multiple carburetors that can be employed is limited because of the dimensional relationship between the vertical pitch of the carburetors and the vertical pitch of the cylinder bores. It is only possible either to employ carburetors having small bore diameters, which are however not preferable from the standpoint of producing higher engine output power, or to employ intake manifold pipes having different lengths. The engines with those carburetors or intake manifolds cannot produce higher engine output power or operate with low responses.
If an array of multiple carburetors is to be used with a bank of engine cylinders, then it is preferable for the carburetors to be coupled to a throttle adjusting link mechanism which should be as simple as possible.
The outboard engine disclosed in the latter publication is free from the aforesaid drawbacks since as many carburetors as the number of cylinder pairs are vertically arrayed. The vertical array of carburetors is suitable for use with engines such as V-shaped cylinder engines which have a space defined between the cylinder banks and which provide a large distance between upper and lower cylinders. However, the vertical array of carburetors cannot easily be combined with engines such as in-line engines whose cylinders are spaced shorter distances from each other. If as many carburetors as the number of engine cylinders are disposed on one side of a vertical in-line engine, the vertical position of the uppermost carburetor is limited by the fly-wheel positioned upwardly of the upper end of the engine block, and the vertical position of the lowermost carburetor is also limited by the lower case of the engine.
The present invention has been made in an effort to effectively solve the above-noted problems of the conventional outboard engines and/or meet the performance demands for outboard engines.